Reference may be made to the following U.S. patents of interest: U.S. Pat. Nos. 3,115,861 and 3,504,503.
In my U.S. Pat. No. 3,115,861, a technique is disclosed to aid in the location of underground facilities, utility lines or elements of construction, such as wires, cables, conduit, sewer pipes and sewer connections, valves, water lines, gas lines, and the like, by digging a trench, placing the utility line or element of construction therein, then placing a readily frangible colored body or tape, the color of which contrasts with the surrounding earth soil above the line or element, and then filling the trench with earth. The contrasting color of the frangible tape acts to alert and caution those digging in the earth soil area that a utility line is present.
In my U.S. Pat. No. 3,504,503, there is described an improved technique in which a sheet of a frangible, flexible metal foil in the form of a tape carries a color to contrast with the color of the earth soil adjacent the utility lines or elements of construction. The metal foil can be detected by conventional types of metal detecting devices from above the earth's surface and, hence, the presence and location of the utility line or element of construction can be ascertained from above the surface of the earth.
Later, it was found desirable to provide printed cautionary wording on the frangible bodies or locating tapes, which cautionary wording identifies the type of utility line or element of construction which is associated therewith. Typically, black lettering is printed directly on the frangible body or tape surface which indicates, for instance, "CAUTION: BURIED GAS LINE BELOW". In addition, it was found desirable to correlate and color code the facility locating tape with the type of underground facility being protected. Thus, a uniform color code was developed and has now been generally accepted in the industry to identify underground facilities as follows: Red--electric power lines; Yellow--gas, oil or steam lines; Orange--telephone, police and fire communications, and cable television; Blue--water lines; and Green --sewer lines.
However, the use of printing on the tape face identifying the type of utility element and the use of a prescribed tape color and color code to identify a particular utility element has led to problems in the use of such utility line locating tape elements. It has been found that the cautionary printing placed on the tape surface is vulnerable to being removed by erasure, rubbing off, chemical activity under the ground by hydrocarbons, and by underground electrolysis. Thus, after a period of time, the cautionary printing disappears from the tape due to scratching or rubbing off, and also due to natural causes from the effect of hydrocarbons, or petroleum present under the ground and this renders the supplied cautionary printing indicia useless as a means of identifying the type of utility element supposedly being protected. Several attempts were made to treat the tape surface prior to printing in order to enable the printing to remain indelible, however none of such experimental techniques have solved the problem.
In addition, in certain instances, the coded tape color corresponding to the associated utility line or element of construction does not form a contrast with the surrounding earth soil sufficient to reliably caution one digging in the soil. For example, when a red colored locating tape associated with electric power lines, etc. is placed in red colored soil such as sandstone or reddish clay, the desired contrast between the locating tape color and the surrounding soil is not present. Similarly, orange coded tapes often do not provide sufficient contrast in desert soils, and green coded and blue coded tapes are often problems in heavily forested or shaded areas. In such instances the utility line may be damaged before one views the cautionary locating tape.
Accordingly, it is desired to provide such a utility line locating tape for underground utility lines which tap is detectable from above the earth surface and which contains printing indicia identifying the type of associated utility line and which printing indicia remains indelible on the tape during normal use. In addition, it is desired to provide such a utility line locating tape in which a contrasting color is provided on the tape along with a coded color associated with the particular underground line element being protected so that there is a sufficient contrast between the tape itself and the surrounding soil even under conditions where the coded color does not form such a sufficient contrast.